Conventionally, in an engine of a compression ignition type such as a homogeneous charge compression ignition (HCCI) type, controlling a burning temperature in a furnace has been important especially during an operation in a high-load range. Hence in the case of adopting an EGR system, in order to be able to control a temperature of an exhaust gas (EGR gas), which is returned to the furnace, in a wider range in the EGR system, it has been desired to improve the cooling performance of the EGR gas.
As one method for providing the furnace with the EGR gas at a lower temperature, for example as described in Patent Document 1, there is an exhaust system device in which the EGR gas is taken out of the downstream side of the exhaust purification device and is then cooled with the EGR cooler and returned to the furnace. In this exhaust system device, the exhaust gas, which is in a rather cooled state by having passed through the exhaust purification device, can be taken out as the EGR gas, so that the EGR gas at a relatively low temperature can be returned to the furnace without the need to significantly enhance the cooling capability of the EGR cooler.